Disposable diapers for infants and incontinent older people are a major industry and as such constitute a crowded art, competitively speaking.
In general, they comprise a liquid-impermeable back sheet and an absorbent pad assembly comprising at least an absorbent pad in the crotch portion and typically also a liquid-permeable cover or front sheet.
While the back sheet must be liquid-impermeable to prevent escape of body waste materials through the back of the diaper, the prior art, as exemplified by the patent literature, has recognized the advisability that it also be breathable for the comfort of the wearer, particularly in warm weather.
In general, the patent literature has taught that this breathability can be obtained in one of two ways: (1) providing a backsheet consisting of a single sheet material which is both breathable and liquid-impermeable; and (2) employing for the back sheet what is in fact two separate films or sheet materials to provide the combination of breathability and liquid-impermeability.
Illustrative of the former are U.S. Pat. No. 3,156,242 of Crowe teaching the concept of employing a microporous film to provide a breathable backsheet; and U.S. Pat. No. 3,989,867 which discloses a breathable backsheet having tapered hollowed bosses which prevent the passage of liquids while permitting vapors to pass therethrough.
As an illustration of the latter, mention may be made of U.S. Pat. No. 4,341,216 issued to Obenour which teaches a two-element breathable backsheet consisting of a vapor pervious, relatively liquid impervious outer sheet and a liquid impervious inner panel. The inner panel is placed between the outer sheet and an absorbent core (pad) in the crotch region. In the embodiment shown in FIGS. 1, 4 and 5 the inner panel 24 is of smaller longitudinal dimension than the outer sheet 25 and is positioned only in the crotch area with the absorbent pad 24 overlapping each longitudinal end section. In the embodiment illustrated in FIGS. 2 and 6, the inner panel 24 is of essentially the same dimensions as the outer liquid impervious sheet, the crotch portion of the inner panel, 28, being liquid impervious and the outer or longitudinal end sections 26, 27 on either side of the crotch section 28 being vapor permeable.
As a further illustration of the latter, mention may be made of U.S. Pat. No. 3,881,489 teaching a breathable backsheet comprising a first layer which is a low void volume perforated thermoplastic film and a second layer which is a porous high void volume hydrophobic tissue.
While not intended to be an search of the patent literature, the following additional patents further illustrate the state of the art pertaining to breathable back sheets: U.S. Pat. Nos. 4,425,128 of Motomura; 4,713,068 of Wang et al.; 4,758,239 of Yeo et al.; 4,777,073 issued to Sheth; 4,818,600 and 4,828,556 issued to Braun et al.; and 4,829,096 of Kitamura et al.
In general the prior concepts for providing both breathability and liquid impermeability suffer from one or more of the following deficiencies: (1) can't provide optimum breathability without sacrifice of the critical requirement for liquid-impermeability to prevent escape of body waste through the back of the diaper; and/or (2) inability to prevent edge leakage through the side edges of the crotch area to soil the leg, clothing, bedsheet and/or other surrounding articles.
With respect to the latter, the prior art, as exemplified by the patent literature, also discloses the separate concept of providing barrier strips and the like along the edges to prevent this edge leakage. Illustrative patents providing such means for preventing edge leakage include U.S. Pat. Nos. 3,349,769 issued to Piekarski; 3,572,342 of Lindquist et al.; 4,610,682 of Kopp; and 4,804,379 of Toth et al.
Stated simply, the task of this invention is to provide a disposable diaper providing optimum breathability while at the same time preventing edge leakage, the diaper being characterized further as being of an elegant and cost-effective design which permits the use of less expensive materials in the manufacture of the back sheet.